The selection of NaHCO3 as growth limiting substrate is purely based on its high concentration in the growth media (Zarrouk’s medium), when compared with other medium constituents. The percentage decrease in the Spirulina (Arthrospira) indica biomass and lethal concentration and time (LCt50) of the toxin (Cd (II)) dosage required to kill half the members of a tested population after seven days of test duration, was calculated.